v8: back-port openbsd/amd64 build fix

Cherry-pick https://codereview.chromium.org/856553002 from upstream.

Makes V8 on OpenBSD/amd64 pick up the right V8_INT64_C and V8_UINT64_C
macros.

PR-URL: https://github.com/iojs/io.js/pull/1318
Refs: https://github.com/iojs/io.js/pull/1312
Reviewed-By: Fedor Indutny <fedor@indutny.com>
Reviewed-By: Johan Bergström <bugs@bergstroem.nu>

deps/v8/src/base/macros.h

@@ -333,7 +333,7 @@ inline void USE(T) { }
 # define V8_INTPTR_C(x)   (x ## LL)
 # define V8_PTR_PREFIX    "I64"
 #elif V8_HOST_ARCH_64_BIT
-# if V8_OS_MACOSX
+# if V8_OS_MACOSX || V8_OS_OPENBSD
 #  define V8_UINT64_C(x)   (x ## ULL)
 #  define V8_INT64_C(x)    (x ## LL)
 # else